Submarine Base Pilings

SUBMARINE BASE PILINGS
- Application of 100% Solids Polyurethane Coatings

A 100% solids polyurethane coating dramatically outperformed a coal tar epoxy system in protecting steel pilings at the Trident submarine base in King's Bay, Georgia over a 5 year period. This case history does not involve tanks but does involve a direct comparison between 100% solids polyurethane and epoxy over an extended period under rather severe service.

During the spring of 1986, the U.S. Navy commenced the construction of its new Trident submarine base. The program involved 200,000 square feet of steel pilings and a similar quantity of pipe pilings. The pilings were coated with a 100% solids polyurethane and the pipe pilings were protected with coal tar epoxy. Both coating systems met the Navy specification 68-81-3020 Sec. 098505. No cathodic protection was used. The pilings were coated by Pennsylvania applicator in the spring of 1986 and installed by South Carolina construction company that fall.

Forty per cent of the pilings supported a permanent infrastructure of docks and piers. The remaining pilings were used to construct a temporary dry-dock facility for use over 5 year period for the rehabilitation of submarines. As part of the Navy's plan, these pilings were removed during the summer of 1990 and scheduled for disposal. During the removal it was discovered that the pilings coated with the polyurethane were in such pristine condition that they could be re-used or sold for a future project. Further inspection of the permanent pilings protected with the 100% solids polyurethane showed that they too were in excellent condition.

The polyurethane exhibited no flaking, brittleness, cracking or delamination after 5 years of abrasion, salt spray and tidal activity. Large sections of the pilings had little or no barnacle growth and where barnacles were located, they were easily removed. There was some spot corrosion where the coating had been gouged as a result of severe abrasion. However, the rust did not extend beyond the damaged areas.

The epoxy pilings coated at approximately the same time with the same surface preparation and exposed to the same service conditions did not fair nearly as well. The epoxy blistered and delaminated in many spots. There were also large areas where the steel had rusted through the coating. The barnacle growth was extensive and difficult to remove.

In 1991, the Port of New Orleans chose a 100% solids polyurethane coating for corrosion protection of the steel pipe pilings for their Nashville Wharf B project. The evaluation after 5 years of service life proved the polyurethane coating is performing superbly.

Minor damage can be found on the pilings from the severe abrasion damage caused by installation and in-service conditions. Even where the coating has been damaged, there is only minimal undercutting. The expansion work continues at The Port of New Orleans. At present, Wharf C is under construction which involves the addition of 1,000,000 square feet to the Nashville Wharf structure.

However, for the Wharf C pilings, the choice was made to go with a lower cost fusion bonded epoxy product. Upon visual inspection, the f.b.e.-coated pilings are not faring as well as those protected with the polyurethane coating.

With the Wharf C construction nearing completion, the f.b.e.-coated pilings have been in service for less than one year and show signs of more than "normal" wear and tear. The inherent brittleness of the fusion bonded epoxy material allows for severe damage to occur to the coating from the impact of the installation hammer.

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